Eucalyptus: Fibre, fuel, biomaterials possible

Professor Zander Myburg, a researcher at the University of Pretoria (UP) in South Africa, was the lead investigator in a global project to unravel the genetic blueprint of Eucalyptus grandis, a species from a genus of fast-growing trees commonly known as ‘bluegum trees’ in South Africa.
The successful sequencing of this genome was published in the prestigious, high-impact scientific Journal Nature earlier this month (June 2014). In explaining the significance of this scientific milestone, Prof Myburgh says: “Now that we understand which genes determine specific characteristics in these trees, we can breed trees that grow faster, have higher quality wood, use water more efficiently and will cope better with climate change,” adding that well-managed Eucalyptus plantations could be turned into bio-factories to produce specific kinds of sought-after materials and chemicals.

“With this new knowledge about the molecular basis for superior growth and specific adaptations in plants, we can apply the same techniques to other woody plants that can be used as feedstock in the bio-economy of the future. Eucalyptus trees are highly adaptable and grow exceptionally fast”

While native to Australia, these trees are planted worldwide, mainly for timber, pulp and paper production, but increasingly also for “dissolving pulp” from which a wide variety of cellulose-based industrial products from textiles to pharmaceuticals are derived. “In future, jumbo jets may take off powered by renewable, Eucalyptus-based fuel,” Prof Myburgh says.

The project to sequence the Eucalyptus grandis genome involved 80 researchers from 30 institutions across 18 countries. It took them five years to sequence and analyse the 640 million base pair genome. Combing through the more than 36 000 genes found in Eucalyptus, the researchers homed in on those that may be able to boost the economic value of the trees by influencing the production of cellulosic raw material that can be processed for pulp, paper, biomaterials and bioenergy applications.

“As one of the lead organisations, the University of Pretoria is delighted with the positive outcomes of the project and the exciting new opportunities for our genomic research programmes,” says Prof Anton Ströh, Dean of the Faculty of Natural and Agricultural Sciences at UP.

Prominent co-leaders on the project includes Prof Dario Grattapaglia of the Brazilian Agricultural Research Corporation (EMBRAPA) and Catholic University of Brasilia; Dr Gerald Tuskan of the Oak Ridge National Laboratory (ORNL) and the BioEnergy Science Center (BESC) and US Department of Energy Joint Genome Institute (DOE JGI); Prof Dan Rokhsar of the DOE JGI and Dr Jeremy Schmutz of the DOE JGI and the HudsonAlpha Institute for Biotechnology.

The US Department of Energy was a major funder via its Joint Genome Institute in Walnut Creek, California, where most of the DNA sequencing was done . South Africa’s Department of Science and Technology (DST), together with forestry companies Sappi and Mondi, supported Prof Myburg and his team by funding the construction of the genome map used as a scaffold for genome assembly, as well as the sequencing of expressed genes used for annotation of the genome.

“The development of new knowledge and skills in tree genomics, and the application of that knowledge to enhance industry competitiveness, is directly aligned with the DST’s vision of a bio-economy”, says Dr Phil Mjwara, Director General of the Department of Science and Technology. “This is a superb example of full value-chain thinking, and thus an important investment for the Department.”

Prof Myburg’s research team identified genes encoding 18 final enzymatic steps for the production of cellulose and the hemicellulose xylan, both carbohydrates that are enriched in wood fibre cells and can be used for biofuel production. “By tracing their evolutionary lineages and expression in woody tissues we defined a core set of genes for biopolymer production that are highly expressed in the development of xylem-the woody tissue that helps channel water throughout the plant and strengthens the tree,” he explains.

Team members Dr Carsten Külheim and Prof Bill Foley at Australian National University (ANU) also found that among sequenced plants to date, Eucalyptus showed the highest diversity of genes for specialised metabolites such as terpenes. These hydrocarbons serve as chemical self-defenses against pests, as well as providing the familiar aromatic essential oils used in medicinal cough drops and in industrial processes.

Among the family of terpene compounds naturally produced in plants and in particularly high abundance in Eucalyptus trees, derivatives of sesquiterpenes that contain 15-carbon atoms (diesel fuel typically contains 10 to 24 carbon atoms) may be promising alternatives for petroleum-based fuels. Researchers have already made important breakthroughs in engineering aspects of terpene biosynthesis into microbes such as bacteria and yeast.

“This means that in future we could use specially selected Eucalyptus genes in bacteria and yeasts, turning them into bio-factories to manufacture advanced biofuels on a large scale,” Myburg says.